U.S. patent application number 11/523002 was filed with the patent office on 2007-03-22 for driving device of motor.
This patent application is currently assigned to SANYO ELECTRIC CO. LTD.. Invention is credited to Keiji Kishimoto, Mamoru Kubo, Kenji Nojima, Kazuhisa Otagaki, Yoshio Tomigashi.
Application Number | 20070063666 11/523002 |
Document ID | / |
Family ID | 37603320 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070063666 |
Kind Code |
A1 |
Kubo; Mamoru ; et
al. |
March 22, 2007 |
Driving device of motor
Abstract
An object is to provide a driving device capable of smoothly
shifting from a starting state to a sensor-less vector control, in
a case where the device drives a motor by the sensor-less vector
control, and the device includes a voltage detecting circuit which
detects an induced electromotive voltage of the motor. A control
circuit starts the motor by rectangular wave control. A magnetic
pole position of a rotor is detected based on an induced
electromotive voltage of one remaining phase of the motor detected
by the voltage detecting circuit. The control circuit controls a
main inverter circuit based on the detected magnetic pole position,
and accelerates the motor by the rectangular wave control. In a
case where a predetermined shift revolution speed is reached, the
control circuit shifts to vector control by the sensor-less in
which the magnetic pole position detected during the rectangular
wave control is used as an initial value.
Inventors: |
Kubo; Mamoru; (Isesaki-shi,
JP) ; Nojima; Kenji; (Ota-shi, JP) ; Otagaki;
Kazuhisa; (Gunma, JP) ; Tomigashi; Yoshio;
(Osaka, JP) ; Kishimoto; Keiji; (Osaka,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SANYO ELECTRIC CO. LTD.
|
Family ID: |
37603320 |
Appl. No.: |
11/523002 |
Filed: |
September 19, 2006 |
Current U.S.
Class: |
318/807 ;
318/799 |
Current CPC
Class: |
H02P 6/21 20160201; H02P
21/34 20160201 |
Class at
Publication: |
318/807 ;
318/799 |
International
Class: |
H02P 27/04 20060101
H02P027/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 20, 2005 |
JP |
2005-271765 |
Claims
1. A driving device of a motor comprising: a main inverter circuit
which applies a pseudo three-phase alternating voltage to a motor
to drive the motor; current detecting means for detecting a current
which flows through the motor; and control means for executing a
sensor-less vector control based on an output of this current
detecting means, the driving device further comprising voltage
detecting means for detecting an induced electromotive voltage of
the motor, wherein the control means starts the motor by
rectangular wave control, detects a magnetic pole position of a
rotor based on the induced electromotive voltage of one remaining
phase of the motor detected by the voltage detecting means,
controls the main inverter circuit based on the detected magnetic
pole position, and accelerates the motor by the rectangular wave
control, and in a case where a predetermined shift revolution speed
is reached, the control means shifts to vector control by the
sensor-less in which the magnetic pole position detected during the
rectangular wave control is used as an initial value.
2. A driving device of a motor comprising: a main inverter circuit
which applies a pseudo alternating voltage to a motor to drive the
motor; current detecting means for detecting a current which flows
through the motor; and control means for executing a sensor-less
vector control based on an output of this current detecting means,
wherein the control means starts and accelerates the motor by a
constant V/F control, and detects a magnetic pole position of a
rotor based on an output of the current detecting means during the
constant V/F control, and in a case where a predetermined shift
revolution speed is reached, the control means shifts to the
sensor-less vector control in which the magnetic pole position
detected just before is used as an initial value.
3. The driving device of the motor according to claim 1 or 2,
wherein when the control means drives the motor at a revolution
speed lower than the shift revolution speed after started, the
control means once accelerates the motor up to the shift revolution
speed, shifts to the sensor-less vector control, and thereafter
lowers the revolution speed.
4. The driving device of the motor according to any one of claims 1
to 3, wherein the control means changes the shift revolution speed
in accordance with a load situation of the motor.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a driving device which
controls a motor by a sensor-less vector control system without
using any magnetic pole positional sensor.
[0002] Heretofore, in a case where a permanent magnet synchronous
motor is operated by a sensor-less vector control, it is necessary
to estimate a magnetic pole position of a rotor without using any
sensor. As an estimating method, there are a method based on a
fundamental wave of an induced electromotive voltage and a method
based on a high harmonic wave, but the method based on the
fundamental wave can only be applied to a medium to high speed
region. That is, the induced electromotive voltage is small in a
stop position and a low-speed region, it is difficult to detect the
voltage, and a high-frequency voltage or current is injected to
generate the high harmonic wave of the induced electromotive
voltage and estimate the magnetic pole position. Therefore, in a
sensor-less system for a high speed, the fundamental wave of the
induced electromotive voltage is utilized. In a sensor-less system
for a low speed, there is utilized a method of injecting the
harmonic.
[0003] In an actual vector control, with respect to a d-q axis
which the magnetic pole position of the rotor of the synchronous
motor is a rotary position at a real angle .theta.d, a dc-qc axis
is supposed in which an estimated angle .theta.dc is obtained in
the control system. An axial error .DELTA..theta. between the axis
is estimated and calculated. So as to set this axial error
.DELTA..theta. to zero, the estimated magnetic pole position is
feed back and corrected, and this allows an actual magnetic pole
position to meet a controlled magnetic pole position.
[0004] According to such a vector control, it is possible to
ideally control a torque generated in the motor by an inverter in
accordance with load conditions, and it is possible to realize a
control of the revolution speed of motor with high efficiency and
precision. Since there is not any sensor-less vector control system
that is usable at low to high speeds, however, there is proposed a
method and the like in which, for example, after the motor is
started under a constant V/F control without the necessity of
detecting the magnetic pole position, the control is shifted to the
vector control using a preset initial magnetic pole position at a
predetermined revolution speed (see, e.g., Japanese Patent
Application Laid-Open No. 2004-48886).
[0005] Moreover, there is also a system in which after starting the
motor, the sensor-less vector control for the low speed is
executed, and the control is shifted to the sensor-less vector
control for the high speed. In this case, there is proposed the use
of the magnetic pole position obtained by weighted-averaging the
positions detected for the low and high speeds in the vicinity of
the switching between the low speed and the high speed (see, e.g.,
Japanese Patent No. 3612636).
[0006] Thus, there are proposed various control systems after the
motor starts until the motor reaches the predetermined revolution
speed at which the detection of the magnetic pole position
(estimation of the magnetic pole position using the induced
electromotive voltage in the sensor-less vector control for the
high speed) is possible in a case where the sensor-less vector
control for the high speed is performed. However, if an axial error
is large between the actual magnetic pole position immediately
after the control has shifted to the sensor-less vector control and
the initially set magnetic pole position, there rises a danger that
the motor runs out of step and fails in starting in the feedback
control.
[0007] Moreover, even in the system in which the sensor-less vector
control for the low speed shifts to the sensor-less vector control
for the high speed as described above, the motor easily runs out of
step immediately after the shifting. Furthermore, in a case where a
load torque is larger or, for example, a case where a difference
between a high pressure and a low pressure of a refrigerant circuit
becomes large in the motor for a compressor to thereby increase
fluctuations of the load torque, the motor easily runs out of step
especially during the shift to the sensor-less vector control
described above.
SUMMARY OF THE INVENTION
[0008] The present invention has been developed in order to solve
the above-described conventional technical problem, and an object
thereof is to provide a driving device which can smoothly shift
from a starting state to a sensor-less vector control in a case
where a motor is driven by the sensor-less vector control.
[0009] The present invention is characterized by a driving device
of a motor comprising a main inverter circuit which applies a
pseudo three-phase alternating voltage to a motor to drive the
motor; current detecting means for detecting a current which flows
through the motor; and control means for executing a sensor-less
vector control based on an output of this current detecting means,
the driving device further comprising voltage detecting means for
detecting an induced electromotive voltage of the motor, wherein
the control means starts the motor by rectangular wave control,
detects a magnetic pole position of a rotor based on the induced
electromotive voltage of one remaining phase of the motor detected
by the voltage detecting means, controls the main inverter circuit
based on the detected magnetic pole position, and accelerates the
motor by the rectangular wave control, and in a case where a
predetermined shift revolution speed is reached, the control means
shifts to vector control by the sensor-less in which the magnetic
pole position detected during the rectangular wave control is used
as an initial value.
[0010] Moreover, a second invention is characterized by a driving
device of a motor comprising a main inverter circuit which applies
a pseudo alternating voltage to a motor to drive the motor; current
detecting means for detecting a current which flows through the
motor; and control means for executing a sensor-less vector control
based on an output of this current detecting means, wherein the
control means starts and accelerates the motor by a constant V/F
control, and detects a magnetic pole position of a rotor based on
an output of the current detecting means during the constant V/F
control, and in a case where a predetermined shift revolution speed
is reached, the control means shifts to the sensor-less vector
control in which the magnetic pole position detected just before is
used as an initial value.
[0011] Furthermore, a driving device of a motor according to a
third invention is characterized in that, when the control means
drives the motor at a revolution speed lower than the shift
revolution speed after started, the control means once accelerates
the motor up to the shift revolution speed, shifts to the
sensor-less vector control, and thereafter lowers the revolution
speed.
[0012] In addition, a driving device of a motor according to a
fourth invention is characterized in that the control means changes
the shift revolution speed in accordance with a load situation of
the motor.
[0013] According to the present invention, the control means starts
the motor by the rectangular wave control, and utilizes the induced
electromotive voltage of one remaining phase to detect the magnetic
pole position of the rotor. Moreover, the control means accelerates
the motor by the rectangular wave control based on this detected
magnetic pole position, and shifts to the vector control by the
sensor-less, when the predetermined shift revolution speed is
reached. In this case, however, as the initial value of the
magnetic pole position during the sensor-less vector control, the
magnetic pole position just detected during the rectangular wave
control is used. Therefore, an axial error between an actual rotor
magnetic pole position and an estimated magnetic pole position can
be minimized, step-out is avoided during the shift to the vector
control by the sensor-less, and a stable control of the driving of
the motor can be realized from the starting till the sensor-less
vector control.
[0014] Furthermore, according to the second invention, the control
means starts the motor by the constant V/F control, accelerates the
motor, and shifts to the vector control by the sensor-less, when
the predetermined shift revolution speed is reached. In this case,
however, a rotor magnetic pole position which is not originally
required is detected beforehand during the constant V/F control,
and as the initial value of the magnetic pole position during the
sensor-less vector control, the magnetic pole position just
detected during the constant V/F control is used. Therefore, the
axial error between the actual rotor magnetic pole position and the
estimated magnetic pole position can similarly be minimized, the
step-out is avoided during the shift to the vector control by the
sensor-less, and the stable control of the driving of the motor can
be realized from the starting till the sensor-less vector
control.
[0015] In addition, according to the third invention, in addition
to the above inventions, when the control means drives the motor at
the revolution speed lower than the shift revolution speed after
started, the control means once accelerates the motor up to the
shift revolution speed, shifts to the sensor-less vector control,
and thereafter lowers the revolution speed. Therefore, even when
the motor needs to be driven at the low revolution speed from the
beginning of the starting, the sensor-less vector control can be
executed without any trouble.
[0016] Moreover, according to the fourth invention, in addition to
the above inventions, since the control means changes the shift
revolution speed in accordance with the load situation of the
motor. Therefore, for example, in a case where a load torque of the
motor, a degree of fluctuation of the load torque or the like is
large, after the control means accelerates the motor up to a higher
revolution speed, the means shifts to the sensor-less vector
control. Accordingly, a danger of step-out can further securely be
avoided. In a case where the load torque is small, when the means
shifts to the sensor-less vector control at a lower revolution
speed, the means can promptly shift to the driving by the
sensor-less vector control with high precision and performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an electric circuit diagram of a driving device of
a motor in one embodiment of the present invention;
[0018] FIG. 2 is a constitution diagram of the motor of FIG. 1;
[0019] FIG. 3 is a flow chart showing a control program of a
control circuit constituting the driving device of FIG. 1;
[0020] FIG. 4 is a diagram showing a voltage of each phase of the
motor during rectangular wave control;
[0021] FIG. 5 is an electric circuit diagram of a driving device in
another embodiment of the present invention;
[0022] FIG. 6 is a flow chart showing a control program of a
control circuit constituting the driving device of FIG. 5;
[0023] FIG. 7 is an explanatory view of a control in Embodiment 3
of the present invention; and
[0024] FIG. 8 is an explanatory view of a control in Embodiment 4
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] Next, embodiments of the present invention will be described
in detail with reference to the drawings. In the following
embodiments, a motor M is an incorporated permanent magnet type
synchronous motor to drive a motor compressor (not shown) which is
to be mounted on, for example, a automobile air conditioner and in
which carbon dioxide is used as a refrigerant. The motor M is
stored together with, for example, a rotary compression element in
a shell of such a compressor, and is used to rotate and drive the
compression element.
Embodiment 1
[0026] First, FIG. 1 is an electric circuit diagram of a driving
device D of a motor M in one embodiment (Embodiment 1) of the
present invention, FIG. 2 is a constitution diagram of the motor M,
and FIG. 3 is a flow chart showing a control program of a control
circuit C as control means constituting the driving device D. The
driving device D of the present embodiment is constituted of: a
main inverter circuit 1 (vector control inverter) including six
switching elements connected to a direct-current power source DC as
a battery of an automobile; the control circuit (control means) C
which controls commutations of the switching elements of this main
inverter circuit 1 to apply a pseudo three-phase alternating
voltage to the motor M.
[0027] Moreover, the motor M is a synchronous motor (FIG. 2)
constituted of: a stator 3 around which three-phase coils 3U, 3V
and 3W are wound by, for example, a concentrated widing; and an
incorporated permanent magnet type rotor 4 which rotates in this
stator 3. The three-phase coils 3U, 3V and 3W of U, V and W-phases
of the stator 3 are connected to secondary lines 2U, 2V and 2W of
phases of the main inverter circuit 1, respectively.
[0028] Furthermore, the secondary lines 2V and 2W of the V and
W-phases are provided with current sensors (current detecting
means) 6V, 6W including current transformers for detecting currents
which flow through the V and W-phases of the motor M, respectively,
and outputs (detected current values) of the current sensors 6V, 6W
are input into the control circuit C. Furthermore, the secondary
lines 2U, 2V and 2W of the phases are connected to voltage
detecting circuits (voltage detecting means) 7U, 7V and 7W
including voltage divider resistances for detecting voltages
induced in the lines, respectively. Terminal voltages (divided
detected voltage values) of the voltage detecting circuits 7U, 7V
and 7W are input into a rectangular wave control position detecting
circuit (constituting the control means) 8. An output of this
rectangular wave control position detecting circuit 8 is also input
into the control circuit C. This rectangular wave control position
detecting circuit 8 or the control circuit C is constituted of a
general-purpose microcomputer. It is to be noted that in the
present embodiment, the rectangular wave control position detecting
circuit 8 is shown separately from the control circuit C, but
needless to say, a function of the detecting circuit may impart to
the control circuit C.
[0029] In this case, the rectangular wave control position
detecting circuit 8 is a circuit for detecting a magnetic pole
position of the rotor 4 in a case where the motor M is rectangular
wave control.
[0030] (Concerning Rectangular Wave Control)
[0031] The rectangular wave control is a so-called 120.degree.
energization system. Only two of the coils 3U, 3V and 3W of the
phases of the stator 3 are energized, and any current is not passed
through one remaining phase. FIG. 4 shows voltages of the phases of
the motor M during the rectangular wave control. In FIG. 4: in a
mode I, a current is passed from the U-phase to the V-phase (any
current is not passed through the W-phase); in a mode II, the
current is passed from the W-phase to the V-phase (any current is
not passed through the U-phase); in a mode III, the current is
passed from the W-phase to the U-phase (any current is not passed
through the V-phase); in a mode IV, the current is passed from the
V-phase to the U-phase (any current is not passed through the
W-phase); in a mode V, the current is passed from the V-phase to
the W-phase (any current is not passed through the U-phase); and in
a mode VI, the current is passed from the U-phase to the W-phase
(any current is not passed through the V-phase).
[0032] In one remaining phase through which any current is not
passed, as shown in FIG. 4, an induced electromotive voltage
appears (tilted line in FIG. 4). Into the rectangular wave control
position detecting circuit 8, the induced electromotive voltages of
the phases (through which any current is not passed) detected by
the voltage detecting circuits 7U to 7W are input. Based on the
initial values, a magnetic pole position estimating signal of the
rotor 4 is obtained by a so-called analog filter system or a
reference voltage comparison system without any sensor. Moreover,
this estimated magnetic pole position signal during the rectangular
wave control is input into the control circuit C.
[0033] During this rectangular wave control, detected positional
information may be obtained every 60.degree., and the current does
not have to be converted into a sine wave. Therefore, the voltage
does not have to be controlled into a sine waveform, and there is
an advantage that a control system can be simplified. However, the
rectangular wave control is disadvantageous in voltage use ratio as
compared with vector control. Moreover, since the control can be
executed only every 60.degree., a control precision is lower than
that of the vector control described later. There is also a
disadvantage that a torque fluctuates more largely.
[0034] (Concerning Vector Control)
[0035] On the other hand, the vector control is a so-called
180.degree. energization system. Since a sine-wave voltage is
applied to the three-phase coils 3U, 3V and 3W of the stator 3 to
drive the motor. Therefore, there are more advantages in respect of
the voltage use ratio and the torque fluctuation as compared with
the rectangular wave control. However, since a current phase is
controlled to be optimum with respect to a magnetic flux of a
permanent magnet of the rotating rotor 4, fine information on the
magnetic pole position is required.
[0036] There will be described hereinafter a method of detecting
the magnetic pole position during the vector control without any
sensor. With respect to a d-q axis (d-axis is a rotor magnetic flux
axis, q-axis is an induced electromotive voltage axis) in which the
magnetic pole position of the rotor 4 of the motor M is a rotary
position (actual magnetic pole position) at a real angle .theta.d,
there is considered a dc-qc axis which an estimated angle .theta.dc
is obtained in the control circuit C. Here, the angle .theta.dc is
prepared in the control circuit C. Therefore, if an axial error
.DELTA..theta. (.DELTA..theta.=.theta.dc-.theta.d) can be
calculated, the magnetic pole position of the rotor 4 can be
estimated.
[0037] In actual, in a case where a motor model formula is solved
in which voltage commands vd* and vq* to be given to, for example,
the main inverter circuit 1 are represented by a winding resistance
r, a d-axis inductance Ld, a q-axis inductance Lq, a power
generation constant kE, a d-axis current command Id*, a q-axis
current command Iq*, a detected q-axis current value Iq, a speed
command .omega.1* and the like together with the axial error
.DELTA..theta., the magnetic pole position of the rotor 4 is
estimated.
[0038] (Concerning Sensor-Less Vector Control)
[0039] The control circuit C executes the sensor-less vector
control of the motor M based on the magnetic pole position of the
rotor 4 detected by such estimation. In this case, the control
circuit C separates the current detected by the current sensors 6V,
6W and flowing from the secondary lines 2V, 2W to the motor M into
a q-axis current component Iq and a d-axis current component Id,
and independently controls the q-axis current command Iq* and the
d-axis current command Id*. For controlling the input speed command
.omega.1*, the control-circuit determines magnitudes and phases of
the voltage commands vd*, vq* so as to maximize the torque in a
relation between a magnetic flux and a current phase, and a
relation between the torque and an operation amount is set to be
linear.
[0040] Moreover, the control circuit C adjusts the phase of the
current flowing through the motor M by use of a detected d-axis
current value Id. Moreover, the circuit gives the voltage commands
vd*, vq* to the main inverter circuit 1, and controls the switching
elements to thereby drive the motor M at a revolution speed which
satisfies the speed command.
[0041] Next, there will be described an operation of the control
circuit C in this case with reference to FIG. 3. In step S1, the
control circuit C outputs the voltage command to the main inverter
circuit 1, and subjects the coils 3U, 3V and 3W of the stator 3 of
the motor M to the above-described rectangular wave control to
generate a rotary magnetic field. The rotor 4 starts its rotation
by this rotary magnetic field. Accordingly, the motor M starts.
From this starting, the control circuit C gives the voltage command
to the main inverter circuit 1 during a constant V/F control
described later to drive the motor M at a constant revolution
speed.
[0042] Next, the control circuit C judges in step S2 whether or not
the magnetic pole position estimating signal has been input from
the rectangular wave control position detecting circuit 8. By a
magnetic pole position estimating method during the rectangular
wave control described above, the rectangular wave control position
detecting circuit 8 estimates the magnetic pole position of the
rotor 4. In a case where a signal is input into the control circuit
C (in this case, about one second, but this differs with the
motor), the control circuit C advances to step S3 to fix the
current phase to a predetermined value in synchronization of the
estimated magnetic pole position, and raises the revolution speed
of (accelerates) the motor M.
[0043] Next, the control circuit C judges in step S4 whether or not
the revolution speed of the motor M has risen up to a predetermined
shift revolution speed X Hz (in actual, 15 Hz to 30 Hz) sufficient
for obtaining the induced electromotive voltage required for
correctly estimating the magnetic pole position in executing the
above-described sensor-less vector control. When the shift
revolution speed X Hz is reached, the magnetic pole position input
from the rectangular wave control position detecting circuit 8 just
before in response to the magnetic pole position estimating signal
of the rotor 4 is set as an initial value. Moreover, the control
circuit shifts to the vector control of the motor M by the
above-described sensor-less vector control by use of the initial
value of this magnetic pole position.
[0044] In this sensor-less vector control, the control circuit C
estimates the magnetic pole position of the rotor 4 during the
above vector control in step S5, and executes a vector control in
step S6. Thus, since the magnetic pole position just detected
(estimated) during the rectangular wave control is used as the
initial value of the rotor magnetic pole position during the
sensor-less vector control, it is possible to minimize the axial
error AO between the actual rotor magnetic pole position and the
estimated magnetic pole position during the shift to the
sensor-less vector control. Step-out during the shift can be
avoided to realize the stable driving control of the motor M from
the starting till the sensor-less vector control.
Embodiment 2
[0045] Next, a second embodiment of the present invention will be
described with reference to FIGS. 5 and 6. Here, in FIG. 5, the
same characters as those of FIG. 1 denote the same or similar
functions. In this case, the above-described voltage detecting
circuits 7U to 7W are not necessary, and the rectangular wave
control position detecting circuit 8 is not used either. Needless
to say, a program of a control circuit C differs.
[0046] Next, there will be described an operation of the control
circuit C in this case with reference to a flow chart of FIG. 6. In
step S10 of FIG. 6, the control circuit C subjects a motor M to
vector control by a constant V/F control to generate a rotary
magnetic field, thereby starting the motor.
[0047] (Concerning Constant V/F Control)
[0048] During this constant V/F control, the control circuit C
controls a speed command .omega.1 and a voltage command V1
beforehand at a constant ratio. The control circuit C gives, to a
main inverter circuit 1, the speed command .omega.1 and the voltage
command V1 obtained from a preset ratio, and drives the motor M.
Since this system does not require magnetic pole position
information of a rotor 4, a control system is remarkably simple,
but there is a disadvantage that a transient vibration is generated
in response to a rapid change of a load.
[0049] After starting such a constant V/F control, the control
circuit C accelerates a revolution speed of the motor M in step
S11. In a case where an induced electromotive voltage required for
executing a sensor-less vector control is obtained by this
acceleration, in step S12, the control circuit C estimates a
magnetic pole position of the rotor 4 by a magnetic pole position
estimating method during vector control. Although the magnetic pole
position information of the rotor 4 is not necessary during the
constant V/F control as described above, the control circuit C
estimates the magnetic pole position, and continues to store the
position during this constant V/F control.
[0050] Next, the control circuit C judges in step S13 whether or
not the revolution speed of the motor M has risen up to a
predetermined shift revolution speed X Hz. When the shift
revolution speed X Hz is reached, the previous magnetic pole
position of the rotor 4 estimated during the constant V/F control
is set as an initial value. Moreover, the control circuit shifts to
a vector control of the motor M by a sensor-less vector control
using this initial value of the magnetic pole position.
[0051] During this sensor-less vector control, the control circuit
C estimates the magnetic pole position of the rotor 4 during the
vector control in step S14, and executes the vector control in step
S15. Thus, since the magnetic pole position just detected during
the constant V/F control is used as the initial value of the rotor
magnetic pole position during the sensor-less vector control, it is
possible to minimize an axial error .DELTA..theta. between an
actual rotor magnetic pole position and an estimated magnetic pole
position in the same manner as in Embodiment 1. Also in this case,
step-out during the shift can be avoided to realize the stable
driving control of the motor M from the starting till the
sensor-less vector control.
Embodiment 3
[0052] Here, during the control of the above-described embodiments,
when a control circuit C receives a speed command at a revolution
speed lower than a shift revolution speed X Hz in a stopped state
of a motor, the circuit once raises the speed up to the shift
revolution speed X Hz, and shifts to a sensor-less vector control.
Thereafter, the circuit lowers the speed down to a target
revolution speed. This behavior is shown in FIG. 7.
[0053] When the control circuit C drives the motor M at the
revolution speed lower than the shift revolution speed X Hz after
starting the motor in this manner, the circuit once raises the
speed up to the shift revolution speed X Hz, and shifts to the
sensor-less vector control. Thereafter, the circuit lowers the
revolution speed. In a case where this control is executed, even
when it is necessary to operate the motor at the low revolution
speed from the beginning of the starting, the sensor-less vector
control can be executed without any trouble.
Embodiment 4
[0054] Moreover, during the control in the above-described
embodiments, a control circuit C changes a shift revolution speed X
Hz in accordance with a load situation of a motor M. As this load
situation, there are considered a load torque, a fluctuation of the
load torque during one rotation, a pressure difference of a
compressor and the like. Moreover, for example, the larger the load
torque of the motor M becomes, the higher the control circuit C
sets the shift revolution speed X Hz. After accelerating the motor
at a higher revolution speed, the control circuit shifts to a
sensor-less vector control. Since step-out easily occurs with a
worse load torque situation (larger load torque), it is possible to
more securely avoid a danger of step-out during the shift by such a
control.
[0055] Furthermore, the smaller the load torque is, the lower the
control circuit C sets the shift revolution speed X Hz. The control
circuit shifts to the control at a lower revolution speed. This
behavior is shown in FIG. 8. In consequence, when the load
situations are not severe, it is possible to promptly shift to
driving of the motor with high precision and performance by the
sensor-less vector control.
* * * * *